1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation represented by deep ultraviolet rays such as a KrF excimer laser and ArF excimer laser, X-rays such as synchrotron radiation, and charged particle rays such as electron beams.
2. Description of Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to increase the degree of integration in recent years.
In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been generally used. However, it is difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays.
Therefore, in order to enable microfabrication with a line width of 0.20 μm or less, utilization of radiation with a shorter wavelength has been studied. Deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.
As a resist applicable to the excimer laser radiation, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter referred to as “photoacid generator”) which generates an acid upon irradiation (hereinafter referred to as “exposure”) has been proposed. Such a resist is hereinafter called a chemically-amplified resist.
As such a chemically-amplified resist, Japanese Patent Publication No. 2-27660 discloses a resist comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. The t-butoxycarbonyl group or t-butylcarbonate group in the polymer dissociates by the action of an acid generated upon exposure, whereby the polymer has an acidic group such as a carboxylic group or a phenolic hydroxyl group. As a result, exposed areas of the resist film become readily soluble in an alkaline developer.
Most of conventional chemically-amplified resists use a phenol resin as a base resin. Deep ultraviolet rays, if used for such a resin as radiation for exposure, are absorbed in the resin due to aromatic rings in the resin and cannot sufficiently reach the lower layers of the resist film. Because of this, the dose of the radiation is greater in the upper layers and smaller in the lower layers of the resist film. This causes a resist pattern profile to be thinner in the upper portion but thicker toward the lower portion, thereby forming a trapezoid shape after development. No sufficient resolution can be obtained from such a resist film. Such a trapezoid resist pattern profile formed after development cannot give a desirable dimensional accuracy in the succeeding steps such as an etching step and an ion implantation step. In addition, if the resist pattern profile is not a rectangle in which the upper side and the sidewall make almost right angle, the resist disappears faster during dry etching, making it difficult to control etching conditions.
A resist pattern profile can be improved by increasing the radiation transmittance through the resist film. For example, a (meth)acrylate resin represented by polymethylmethacrylate is a highly desirable resin from the viewpoint of radiation transmittance, because the (meth)acrylate resin has high transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 4-226461 discloses a chemically-amplified resist using a methacrylate resin, for example.
However, this composition has insufficient dry etching resistance due to the absence of an aromatic ring, although the composition excels in microfabrication performance. This makes it difficult to perform etching with high accuracy. Therefore, a composition having both transparency to radiation and dry etching resistance cannot be provided.
As a means to improve dry etching resistance of the chemically-amplified resist without impairing transparency to radiation, a method of introducing an aliphatic ring into the resin component in the resist instead of an aromatic ring is known. For example, Japanese Patent Application Laid-open No. 7-234511 discloses a chemically-amplified resist using a (meth)acrylate resin having an aliphatic ring.
This resist includes groups which comparatively easily dissociate by conventional acids (acetal functional groups such as tetrahydropyranyl group, for example) and groups which are comparatively difficult to dissociate by acids (t-butyl functional groups such as t-butyl ester group or t-butylcarbonate group, for example) as acid-dissociable functional groups in the resin component. The resin component having the former acid-dissociable functional groups exhibits excellent basic characteristics as a resist, in particular, superior sensitivity and excellent pattern profile, but has poor storage stability as the composition. The resin component having the latter acid-dissociable functional groups has excellent storage stability, but exhibits impaired resist characteristics such as sensitivity and pattern shape. Moreover, inclusion of aliphatic rings in the resin component of this resist results in poor adhesion to substrates due to the extreme increase in hydrophobicity of the resin.
When forming a resist pattern by using a chemically-amplified resist, a heat treatment is usually performed after exposure in order to promote the dissociation of the acid-dissociable functional group. The line width of the resist pattern is inevitably changed to some extent as the heating temperature is changed. However, in order to deal with a recent decrease in size of integrated circuit devices, development of a resist which shows only a small change in line width due to a change in heating temperature after exposure (specifically, temperature dependency) has been demanded.
In addition, the photoacid generator is known to greatly affect the functions of a chemically-amplified resist. Presently, onium salt compounds which generate an acid upon exposure at a high quantum yield and exhibit high sensitivity are widely used as a photoacid generator for chemically-amplified resists.
As the onium salt compounds, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium naphthalenesulfonate, and cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate are used, for example. Most of these conventional onium salt compounds, however, do not exhibit satisfactory sensitivity. Although some compounds may exhibit comparatively high sensitivity, they are not necessarily satisfactory in overall resist performance such as resolution, pattern profile, and the like.
In view of development of technology capable of dealing with a recent progress in microfabrication of integrated circuit devices, a chemically-amplified resist which is applicable to short wavelength radiation represented by deep ultraviolet rays, exhibits high radiation transmittance, and excels in basic characteristics as a resist such as sensitivity, resolution, and pattern profile has been strongly demanded.